Lately it has been attempted to gain the same end by introducing the stick only into the piece to be fired ; by discharging the rocket in this manner, in fact, from a musket. But this is almost equally dangerous, as the composition will not bear the blast which issues from the mouth of the piece, even at that distance. The mo ment it cracks, the fire enters from the bore into the fissures, so as to set fire to more composition than there is vent for ; in concequonoo of %which, an explosion is un avoidable.
The only safe method of gaining this end is by means of a balisla, or cross bow. It was by this machine that the Saracens and others threw their fireworks, as we mentioned in the historical part of this article ; nor can there be any difficulty in applying it to the rocket. The balista should be formed on the same principle as the cross bow, with a steel spring, and a sufficient force of machinery to bring it to the bearing. The trigger is to be provided with a string, for the purpose of dis charging it at a proper distance. Where bow-string comes near to the fire of the rocket, it should be guard ed by a copper wire; but it would be still preferable to use strings made of the best German wire, twisted manifold. In place of one string also, two may be used, connected in the middle by a solid plate of metal, where the fire might reach so as to injure it. This balista has ofor its support a bar of sufficient size and strength to r receive the rocket, and furnished with loops, also, for the purpose of retaining it in its proper position, as it flies off. In firing, however, care must be taken that no blow, or impulse, he given to the rocket, for fear of shaking the composition, and producing the effects above mentioned ; but that the contact of the string should be perfect, that it may pass off the support without a shock. It is scarcely necessary to observe, that the priming must be lighted before the trigger is pulled ; and the composition ought, indeed, to burn for at least half a second before the 'rocket is dis charged.
Of other Uses to which Rockets have been applied.
In our remarks hereafter on the iron rockets, under the military branch of Pyrotechny, we have mentioned their uses in the whale fishery.
We have only here, therefore, to notice a project foe rendering them of use, as just mentioned, in relieving ships in cases of going on shore. The original project of this nature was formed, and not only formed, but published and practised by Lieutenant Bell, of the Royal Artillery. It was, however, neglected by those
who ought to have taken an interest in it, but was af terwards revived by Mr. Manby, who obtained from Parliament the splendid reward which, if any where, was due to the inventor. This consisted in throwing a line out of a piece of ordnance, attached to a shot. If, from the shore to the vessel, the elevation was so given as to cause the shot to range beyond it, so as that the line might fall on board across the ship. If, from the vessel, this precaution was unnecessary ; and in case of any vessels being acquainted with this expedient, and having the requisite implements on board, the chances of success were, perhaps, somewhat greater. It must be recollected, however, that very few coasting or trading vessels are provided with a piece of ordnance; and that, even if they were, it must generally be impos sible to use it, under the circumstances in which a vessel is aground on a lee shore.
Lately, us an improvement on this method, the same Mr. Manby and a Mr. rengrouse have proposed the use of a rocket. A small line is attached to it below, which is carefully coiled up like a whale line, so as to deliver freely. Being thrown on board the vessel in such a state, it may be made use of to attach a stronger line to, and so on in succession, till a hawser can be carried on shore. It is evident that this project is more applicable than a piece of ordnance, if it is to be carried by the ship ituoif, if fie,. ran be at all pro duced, a rocket may be discharged under any circum stances.
Causes of the Flight of Rockets.
There needed not to have been much dispute on this subject at any time, as the causes of the ascent or flight of a rocket ought to have been sufficiently evident. Yet, when such philosophers as Lemery, Wolf, Pa pin, and many others, considered that the explosive, or expansive force of gunpowder, depended on the ra refaction of air contained in the intersties of the grains; when John Bernouilli imagined that it contributed part of the force; when Muschenbroek, Stahl, Beaume, and Macquer, consider that this effect arose from the con version of the water of the nitre into steam, whereas nitre contains no water ; when Count Rumford fol lowed in the same track ; when Lombard added to thisl the conversion of the nitric acid into vapour ; and when, lastly, others attributed the elastic force of gunpowder to the radiation of disengaged caloric, it is not very surprising that the cause of the flight of a rocket should have been as much misunderstood.